var menu = document.querySelector(".header-menu");
var div = document.querySelector(".menu-content");
var mark = true;
menu.addEventListener("click", function () {
    this.className = mark ? "header-menu menu-x" : "header-menu menu-y";
    if (mark) {
        div.style.display = "block";
    } else {
        div.style.display = "none";
    }
    mark = !mark;
})